1. Field of the Invention
The present invention relates to a regulator system with automatically switching pulse skipping mode, and more particularly relates to a pulse width modulation regulator system with automatically switching pulse skipping mode.
2. Description of the Prior Art
In the switching mode regulator, the pulse width modulation (PWM) is extensively used in the method of voltage transformation. When the circuit is needed to provide voltage during the heavy load, the inductor current of the circuit is maintained in the Continuous Conduction Mode (CCM). And the switching speed of PWM is high enough to provide higher power density for heavy load. However, when the circuit is only needed to provide voltage during light load, the inductor current of the circuit is maintained in the Discontinuous Conduction Mode (DCM). And the switching speed of PWM is low enough to provide lower power density for light load.
In the prior art, the PWM regulator is only needed to provide low voltage for light load. In order to reduce the power switching loss, the solution of the prior art is to use pulse skipping mode (PSM) to reduce the number of times to turn on or off the switch in the circuit and achieve the power saving. The PWM regulator with PSM in the prior art, when the circuit is operated in the Continuous Conduction Mode, the output voltage will come with bigger pulse because of the PSM and the phase is not stable.
The traditional asynchronous step-down converter with PSM is shown in FIG. 1. The circuit comprises an error amplifier 100, a comparator 103, a ramp generator 106, a pulse generator with minimum-on-time 109, an OR gate 112, an activator 115, a switch SW1, a diode D1, an inductor L1 and a capacitance C1. In the traditional circuit of FIG. 1, the circuit is added a pulse generator 109 with minimum-on-time to have the pulse skipping mode and save the power. And the inductor current of the circuit can be in the Continuous Conduction Mode (CCM) or the Discontinuous Conduction Mode (DCM). Because the Continuous Conduction Mode (CCM) is not exited in the traditional circuit and the circuit will be adaptively turned off the pulse skipping mode, the switching ratio of the input voltage and the output voltage is very high in the circuit. And the output voltage will be big because of the PSM and the phase will be not stable.
FIG. 2 is a traditional Asynchronous step-up converter with pulse skipping mode (PSM). The circuit comprises an error amplifier 200, a comparator 203, a ramp generator 206, a pulse generator 209 with minimum-on-time, an OR gate 212, an activator 215, a switch SW2, a diode D2, an inductor L2, and a capacitance C2. In the traditional circuit of FIG. 2, the circuit is also added a pulse generator 209 with minimum-on-time in order to have the PSM and save the power. And the inductor current of the circuit can be Continuous Conduction Mode (CCM) or Discontinuous Conduction Mode (DCM). Because the Continuous Conduction Mode (CCM) is not exited in the traditional circuit and the circuit will be adaptively turned off the pulse skipping mode, the switching ratio of the input voltage and the output voltage is very high in the circuit. And the pulse of the output voltage will be big because of the PSM and the phase will be not stable.
Because of the reason described above, the circuit can be operated in Discontinuous Conduction Mode (DCM) to save the power because of the pulse skipping mode (PSM). However, when the circuit is operated in the Continuous Conduction Mode (CCM), the pulse of the output voltage is too big and the phase is not stable. It is necessary to provide a method or system with an operative mode to enable or disable the pulse skipping mode.